Regulus knew Voldemort would be suspicious of him if Peter told him he had been the one to tell the order, so to gain his trust he took missions... lots of them.
And when Voldemort had told everyone at a death eater meeting that he would need help with something, he volunteered Kreacher, he thought it would be an innocent mission, but when his house elf came back half dead he knew something was up.
"Master Regulus! Oh how I wished you would be there" Kreacher cried as Regulus ran to help him.
"What happened Kreacher?!" Kreacher staggered trying to get up.
James wasn't expecting to get a letter from Regulus, he hadn't even seen him since... that day, the order was trying to figure out what to do with the information about Peter when Regulus' owl came through the window and delivered letters to both him and Sirius.
The order stared at them waiting for them to open it, James took his and inspected it, it had the Black family emblem on the front and 'Jamie' written on the back, prompting James to quickly open it.
'Dear James
I know we aren't really on speaking terms since... 6th year, but I wanted to say this.
I'm going on a personal mission, it's definitely stupid and I'm probably going to die. But I wanted you to know that I love you, I've been in love with you since our first date in Hogsmeade, probably before that... since our meet ups at the top of the astronomy tower, I will always love you never doubt that.
I hope when this stupid war is over you will find someone you love, and have a family, like you always dreamed of.
Yours, Reggie'
James looked up at Sirius watching him read the letter with a indescribable face, he threw the note on the table before apparating to Regulus' room in the Black manor.
"What the fuck?!" Regulus stared at James who was standing with a hand on his hip and a livid expression.
"Don't you what the fuck me Regulus, what the fuck you! You think you could send me a god damn suicide note and think I'd be okay with it?!" Regulus looked down on his bed to the fake locket he had prepared for the mission.
"I'm sorry... but I have to do this" James' face softened and he walked up to Regulus before hugging him.
"I'm coming with, and... I love you too"
______
Getting closeeeeee